Certain laser systems perform laser processing operations on target materials, such as trimming thin-film resistors or repairing defective integrated circuits. The following background information is presented herein only by way of example with reference to the use of a compact Q-switched YAG laser to trim a thin-film resistor.
A thin-film resistor typically is made from nichrome or tantalum nitride and has a depth of typically less than 1.0 micron. The geometry of a trimming path in an electrically conductive material affects the resistance value of the thin-film resistor. To provide a thin-film resistor of a desired value of resistance, a trim may, therefore, require either a non-linear path, which would often be of sinusoidal shape, or two or more non-parallel straight line paths, which would often be orthogonal to each other. The resulting trim should be relatively smooth and continuous along the length of the trimming path to prevent unpredictable variations in resistance.
Recent advances in laser technology favor the use of compact diode-pumped Q-switched lasers over arc-pumped lasers in most laser processing applications. (A design description of compact diode-pumped Q-switched laser is set forth in U.S. Pat. No. 4,761,786 of Baer.) For example, unlike arc-pumped lasers, diode-pumped lasers are generally smaller and offer more reliable light pulse emissions. Diode-pumped lasers are also more durable, require considerably less operating power, and eliminate the need for a water cooling system. The use of such a laser to perform trimming operations is, therefore, advantageous and desirable.